Chemical plant parts, gas turbines and the like are typically manufactured using superalloy ingots. Since various types of parts, including rotors of gas turbines and the like, frequently lead to serious accidents if they become damaged during the course of use while also causing considerable losses to be incurred as a result of such damage, superalloy ingots are required to demonstrate particularly severe soundness. Consequently, secondary ingots offering even greater soundness are manufactured by ESR in which primary ingots obtained by melting and casting superalloys are used as electrodes.
In order to manufacture sound secondary ingots by ESR using primary ingots of superalloys as electrodes, a primary ingot of superalloy is first used as an electrode to generate an arc between this electrode and a starter plate, flux is melted by this arc heat to form molten slag, and once the molten slag is formed, a current is applied to the molten slag while redissolving the superalloy primary ingot electrode by using the molten slag as a resistance heating element. Liquid droplets of the remelted superalloy settle due to differences in specific gravity within the molten slag, and the remelted superalloy is refined by the molten slag as it settles; thereby, promoting removal of inclusions and desulfurization. Moreover, a metal pool directly beneath the molten slag undergoes directional solidification by a water-cooled copper mold, enabling the structure to be controlled and allowing the production of a secondary ingot having even greater soundness.
The aspect of the aforementioned ESR procedure that requires the greatest expertise is the task of generating an arc at the start of ESR and dissolving the flux to form molten slag. In this procedure, unless sufficient arc is generated for dissolving the flux, ESR may fail to start, and in the case of such failure, the important, large primary ingot electrode including superalloy, the slag and the start material must be removed and repositioned; thereby, requiring considerable time and labor for restarting ESR. Thus, failure to start ESR must be avoided whenever possible.
On the other hand, an arc start material is known to be typically used in order to start ESR with a stable arc, and examples of arc start materials used include metal powder, metal wool, cut wire and start blocks. These arc start materials such as metal powder, metal wool, cut wire and start blocks are known to be used by mixing with flux (see Patent Documents 1 and 2).    Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H6-262347    Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H6-265570